1. Technical Field
The present invention relates to improved packaging techniques for optical communications systems and, more particularly, to optical packaging techniques utilizing molded leadframe arrangements.
2. Description of the Prior Art
There exist many different arrangements for packaging optical communication arrangements. For example, the optical device (e.g., laser, LED or photodiode) may be attached to a mount which is subsequently aligned with and attached to a base member, the base member utilized to facilitate coupling of an optical fiber to the optical device. In most cases, the base member will include a lensing element to maximize the optical coupling. The arrangement of the mounted optical device, base member and lens is often referred to in the art as an "optical subassembly", or OSA. The electronics required for operating the optical device (a driver circuit for a transmitter or an amplification and decision circuit for a receiver, for example) may then be separately assembled (on a printed wiring board, for example) and connected to the optical subassembly by conventional electrical leads. Alternatively, the electronics may be fully enclosed in a separate housing, with only the leads exposed for connection to the optical subassembly. An advantage of using separate housings for the electronics and optics relates to the ability to interchange the components as required for different applications. For example, a data link application may operate with TTL electronic signals, and another application (with the same optics) may utilize ECL electronic signals. Additionally, if either the electrical or optical portion of an arrangement were to experience a failure, the working portion could be disconnected and re-used with another arrangement. A major disadvantage of separate packaging is the overall size of the resultant arrangement. With two separate packages, the arrangement requires a rather large space. Further, such an arrangement is susceptible to electrical noise introduced by the necessarily long lead lengths between the electronics and the optical device. The electrical noise factor becomes a significant concern at bit rates exceeding approximately 10 Mb/s. Also, long leads may limit the maximum bit rate of either a transmitter or receiver, due to parasitic lead inductance (limits transmitter) or parasitic capacitances (limits receiver).
These and other concerns have led to the development of package designs which provide for the electronics and optical device to be housed in the same unit. Many of these unitary packages are relatively expensive, as a result of using a hybrid integrated circuit (HIC) arrangement for the electronics, with an optical subassembly attached to the HIC. Additionally, the piece parts used in the optical subassemblies associated with these packages are often formed of machined metallic components, adding to the cost of the system. Fabrication problems may also exist with respect to mating the various piece parts (i.e., outer housing, optical subassembly and HIC). Lastly, in many instances, the packaging processes for a transmitter and receiver are often very distinct, leading to manufacturing problems and increasing the overall expense of the packaged system.
An improved package design is disclosed in U.S. Pat. No. 4,911,519 issued to W. H. Burton et al. on Mar. 27, 1990. In the disclosed arrangement, the HIC of a conventional package is replaced by a conventional 16-pin dual-in-line package (DIP) which includes a specialized pair of end prong leads for attachment to the optical subassembly (OSA). The DIP and optical subassembly are subsequently assembled within a plastic molded package frame. The plastic molded frame is configured to include a molded optical connector receptacle for subsequent attachment of a connectorized optical fiber. The arrangement is subsequently covered with a metallic lid which is grounded to the package floor. A significant savings is realized by the utilization of the DIP, as well as utilizing a molded plastic piece part for the frame/connector assembly.
Although the Burton et al. arrangement is considered to be a significant advance over the prior art, the need remains to further simplify optical packaging techniques, with respect to limiting the number of separate assembly operations, in light of rapidly growing markets which will require many thousands of such devices in as a cost competitive arrangement as possible.